In recent years, handheld terminal devices such as notebook-sized personal computers, cellular phones, and PDA (Personal Digital Assistant) are remarkably widespread. As a secondary battery used as a power source for these handheld terminal devices, e.g., a nickel-metal hydride secondary battery and a lithium ion secondary battery are often used. The handheld terminal devices are required to have a comfortable portability, and therefore such devices are rapidly becoming smaller, thinner and lighter with better performance. As a result, the handheld terminal devices are now being used in a wide variety of situations. Like the demand on the handheld terminal devices, there also is a demand on the secondary battery to be smaller, thinner and lighter with better performance.
For improving the performance of the secondary battery, there have been made studies on modification of the electrode, the electrolytic solution, and other members of the battery. Among them, the electrode is usually produced by mixing an electrode active material and, if necessary, an electroconductive material such as electroconductive carbon with a liquid composition in which a polymer that serves as a binder (binding agent) is dispersed or dissolved in a solvent such as water and an organic solvent, to prepare a slurry composition, and applying the slurry composition onto a current collector, and then drying the slurry composition.
As the solvent, an organic solvent has often been used in prior art. However, use of the organic solvent causes problems such as cost required for recycling the organic solvent, and necessity for ensuring safety in using the organic solvent. Therefore, in recent years, production of an electrode using water as the solvent has been studied (see Patent Literatures 1 to 6).